We are conducting a study to examine whether women who have been exposed to chlorinated pesticides or PCBs have alterations in their ovarian function as measured by the frequency of menstrual cycle disturbances. Such disturbances may impact the frequency of infertility and sub-fertility, as well as that of other hormone-dependent illnesses such as breast cancer and osteoporosis. The target population is a group of Laotian immigrants who are frequent consumers of fish caught locally in the San Francisco Bay. Contaminant levels above health protective advisories have been documented in Bay fish and shellfish for a number of these substances. Immigration from Asia, as well as consumption of contaminated fish, have been shown to be associated with higher organochlorine pesticide body burdens. Exposure is determined by measuring serum levels of a panel of pesticide metabolites, including those of DDT, chlordane, hepatochlor and others, as well as PCB congeners. In addition, mercury levels are measured in the blood. Menstrual function is assessed by measuring urinary metabolites of steroid hormones daily during three menstrual cycles of 50 Laotian women of reproductive age. The participants were also asked to complete two detailed in-person interviews about various factors, including fish consumption.